The principle objective of these studies is the understanding of the molecular mechanism and physiologic functions of ion transport across cell membranes. The present work concerns the passive transport of small inorganic anions, chloride, bicarbonate, phosphate, etc., across the human erythrocyte membrane. This process is believed to be carrier mediated and is dependent on the integrity of a 95,000 dalton protein which spans the phospholipid core of the membrane. The investigation of the kinetic characteristics of chloride transport in intact erythrocytes and ghosts suggests that halogens, bicarbonate, nitrate and divalent anions, sulfate and phosphate, share this common mechanism. Thus, the Hamburger shift of chloride and bicarbonate across the membrane while the erythrocyte traverses tissue and lung capillaries is mechanically coupled and facillitated by this selective transport mechanism. Present studies use the methods of tracer kinetics, surface chemistry, artificial lipid bilayers, and protein biochemistry to incorporate the carrier into a well-defined membrane system and thus reconstruct this anion transport mechanism from its components. BIBLIOGRAPHIC REFERENCES: Abstract. R.B. Gunn, S.T. Feldman, and J.M. Horton. Inhibition of chloride transport in human red blood cells by diuretics. Fed. Proc. 36, 564, 1977. Abstract. B. Sarkadi, D.C. Tosteson, G.N. Pandey and R.B. Gunn. Characteristics of Li ion-transport in human red cells. Fed. Proc. 36, 564, 1977.